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Gene therapy for Erythropoeitin
Introduction Some world class athletes have started using gene therapy to gain an advantage over their competitors, generally coined gene doping. One of the more common forms is the enhancement of erythropoeitin (EPO) receptor 1. The enhancement of the EPO receptor increases the mass of red blood cells because the normal regulation is gone. EPO is a hormone secreted by the kidney into the bloodstream during times of hypoxia and anemia. Once EPO reaches the bone marrow red blood cell production is stimulated and apoptosis of both mature red blood cells and red blood cell precursors is inhibited. People suffering from renal failure and HIV can have severe anemia because of the decreased production of EPO 2,3,4. The Leiden group set out to improve the current therapy, biweekly injections of recombinant EPO intramuscular (im) injections back in 1997 2. It has since been used in many studies to encourage healing after traumatic events 3,4 Gene Therapy Approach Svensson et al. looked at the safety and efficacy of using EPO as a potential treatment for serve anemia in two animal models, incompetent mice and cynomolgus monkeys. To deliver the gene they used replication-defective adenovirus under transcriptional control of elongation factor 1-alpha promoter. The plasmid was given to the animals via im injection. They found treatment was dose responsive, with the threshold dose in both mice and non-human primates was 2.5-8X107 pfu/gram. At this dose transgene production was prolonged to 60-90 days in the primate model, and about 1 year in the mouse. They monitored the lungs and liver of the monkeys and did not detect any toxicity. They judged the safety by monitoring the lungs and liver because previous attempts via intravenous and inhaled routes of exposure did not go so well 1. Limitations before human trials: * Doses for humans- extrapolation from mouse and monkey model- at the highest dose 4X1011 pfu the monkey had too many red blood cells. The therapy is contained in the muscle though so it is safer than previous studies. If they were to be a negative reaction the muscle could be removed before wide spread damage/reactions occurred. * Designing a adenovector that they are able to regulate by hypoxia or Tet. 1 Hypoxia is a normal regulator of EPO 2,3 so this form of regulation would seem to be ideal. * Also found significant antibodies in the blood therefore re administration of the plasmid will probably not be effective. 1 Currently EPO is being used as a cytoprotectant for chemotherapy patients and to aid in wound healing, especially in diabetics. These methods involve and injection of the recombinant protein and not the gene. It is actively being researched because of the clinical necessity. The use of EPO is very controversial. There is conflicting evidence of the safeness of the drug 3,4. EPO is involve in the promotion of angiogensis and has been suggested to cause tumor growth in certain cancer patients 3. EPO is also abused by athletes 1. Impact on Athletes EPO is one of the many synthetic hormones used by athletes to increase their performance. EPO will increase their aerobic output but not muscle mass, so it is generally abused by endurance athletes 1,6. It is believed the currently athletes are only able to use recombinant protein therapy which is easily detected. If a transgene therapy were made available it would make detection much more difficult 6. Currently there are PCR protocols being developed to detect transgenic EPO. It would be necessary to use PCR because the increased hormone would appear endogenous since it was translated in their cells. This is still a very difficult task because PCR primers and DNA from the injection (it would have to be the site of injection) are needed 5. All of the research going into detecting EPO abuse is not only to try to keep sports fair but also because it is very dangerous to increase EPO levels. It is still a controversial drug to administer under appropriate conditions but for healthy individuals the risks are elevated. Side effects include 1,6: * blood clotting * too many red blood cells leading to decrease viscosity * increased risk of stroke * myocardial infarction These are all very dangerous events that can lead to death. It seems surprising that there is such an epidemic of EPO use in athletics. These side effects also suggest why therapeutic use is also heavily debated. References 1 Adam, D. 2001. Nature. 414:569-70. PMID:11740511 2 Svensson, E.C. et al. 1997. Human Gene Therapy. 8:1797-1806. PMID:9358029 3 Hamed, S. et al. 2014. Wound Repair Regen. 22:23-33. PMID:24471742 4 Gobe, G.C. et al. 2013. J Nephropathol. 3:154-65. PMID:24475445 5 Perez, I.C. et al. 2013. Anal Bioanal Chem. 405:9641-53. PMID:23912835 6 P. McCrory. 2003. Br J Sports Med. 37:192-3. PMID:12782540